The present invention relates to a controller used in a system for automatically filling cylinders or tanks with a single compressed gas or a mixture of compressed gases, such as oxygen, nitrogen, argon, helium and carbon dioxide and, particularly, to such a controller which is field-configurable to match the specifics of the user's system and to accommodate changes thereto. The present invention is an improvement of the automatic filling system disclosed in our copending application Ser. No. 09/022,318, filed Feb. 11, 1998, entitled "Controller for Tank Filling System", the disclosure of which is incorporated herein by reference.
Gases such as oxygen, nitrogen and argon have widespread use throughout industry and medicine. Manufacturing companies and hospitals commonly purchase their needs of gases from gas distributors that take liquefied oxygen, nitrogen, argon, etc. from large storage tanks and deliver them as gases to smaller containers, which are usually cylindrically shaped and, therefore, are commonly referred to as "cylinders." Accordingly, hereinafter, the word "cylinders" will be used to refer to containers of the type to be filled with the systems controlled by the controller of the present invention, but it will be understood that the invention is applicable for filling containers having shapes other than cylindrical. The distributors usually own the cylinders and send the cylinders filled with compressed gases to their customers. When the cylinders are spent, they are returned to the gas distributor, who refills them with compressed gas.
For many years, the process of filling the cylinders with gases or gas mixtures was performed manually. The gas distributor would have large storage cylinders filled with liquefied gases, such as oxygen, nitrogen, argon, carbon dioxide and helium. Via a manifold, he would simultaneously fill ten, twenty or more cylinders. As a first step, the cylinders were vented, meaning that whatever gas was in the cylinders was bled off. Usually a vacuum pumping system was connected to the manifold to draw a vacuum to evacuate the cylinders. Often one or more purges were performed, meaning, using a different pumping system, the cylinders would be filled with some of the compressed gas, which was then vented. Then, the cylinders were again evacuated. This purging cycle could be repeated as many times as was necessary with whichever gas was necessary to achieve the desired purity of the cylinders. Finally, the cylinders were filled with the specified gas or gas mixture to a predetermined pressure at a stated temperature.
In the process of making gas mixtures, two predominant methods existed. One method was to fill the cylinders with each gas to a different partial pressure to obtain the desired gas mixture ratios. The other method was to weigh in different amounts of various gases to obtain the desired gas ratios. In performing these various steps, the operator would monitor the temperature of the cylinders and the pressures in the system and, in some cases, a scale representing the weight of the gas in the cylinders. For example, when the cylinders were vented, the operator would monitor the pressure in the cylinders and when it reached a predetermined level, he would know it was time to start the evacuation process. Again, he would monitor the pressure to determine when the next step would be taken. The entire process was very time consuming and resulted in much lost time for the operator and the equipment. Also, the pumps, which were expensive, were used only a small fraction of the day.
It has been recognized that computer control of the filling process would substantially reduce the time it would take to vent, evacuate and fill cylinders, and thereby increase the number of cylinders that an operator could fill during a given time period. There are computerized systems in the marketplace. They are usually made for a particular system to fill cylinders with a particular gas or gas mixture. Such a system often incorporates one or more fill pumps for each manifold and a vacuum pump for each manifold. With this type of system, one group of cylinders is filled with one gas or mixture through one manifold, while another manifold is used to vent and evacuate another group of cylinders. A gas distributor tells the manufacturer of the controller which conditions he plans to utilize and then the manufacturer programs the computer to match the distributor's configuration. Other information is added to the computer program by the manufacturer, such as details on the performance characteristics of the pressure and temperature transducers, the electronically controllable valves, etc.
Thus, the manufacturers of currently available controllers make each controller to the order of the customer, each with a particular computer program. If the gas distributor's needs change, e.g., he wants to purchase a different pressure transducer because the original one is no longer operable, or he wants to adjust operating parameters, currently available controllers would have to be reprogrammed by the manufacturer.
Furthermore, presently available computerized systems do not provide automatic purging, where purging is desired, for a selected number of purging cycles with a selectable gas. Also, they do not calculate the weights of each gas add for gas mixtures requested by the customer, nor do they calculate maximum fill pressures when condensable gases are involved in the mixture, and automatically recalculate the fill weights based on the new pressure limit. Presently available systems must have the gas mixture formulas constantly adjusted as changes in the equipment, operation and environment change. This requires constant operator attention. Also, they do not leave the option for either automatic calculation or manual entry.
Gases used for medical purposes, such as those used in hospitals, are considered drugs and, therefore, are regulated by the Food and Drug Administration ("FDA"). The FDA specifies steps to be performed to achieve a certain level of purity and to check the integrity of the cylinders, and requires reports which must comply with certain FDA regulations. In prior systems the purification and integrity checking must be manually monitored and reports must be manually prepared.